Emergency Light

An emergency light is an integral part of household electronics nowadays. We all know an Emergency light is used during a power failure to light up the home. As it is used during a power failure, it should last long, hence generally bright white LEDs are used in emergency lights, because they produce more light and consume less power. Emergency light is a very useful and popular project in the DIY section. So today we are going to build a simple and cost-effective emergency light project.

In this emergency light circuit, when the Power goes OFF, the emergency light activates automatically. We have used four bright white LEDs, more LEDs can be added to produce more light, considering that the total current consumption should not exceed the supply current. Ultra-bright white LED consumes 3V and 20mA of current.

Circuit Diagram of Emergency Light - Explanation

We can divide this LED emergency light circuit into two parts; the first part is used to drop down the 220V AC voltage into 8v regulated DC, with the help of a transformer and a bridge rectifier. And second part consists of a Relay and a rechargeable battery, which is used to light the LEDs during a power failure.

Components Required for Emergency Light Project:

• Transformer- 9-0-9 500mA
• Bridge rectifier
• Diode- 1N4007
• IC 7808 voltage regulator
• Capacitor 1000uF, 0.01uF
• Relay- 6v
• Resistors- 100 ohms
• LEDs- Ultra-bright white LED
• Rechargeable 6v, 4.5Ah Battery

Power Supply Design for Automatic LED Emergency Light Project

In the first part of the circuit, we have used Transformer 9-0-9 500mA, to step down the 220 voltage into 9V. A bridge rectifier is a combination of 4 diodes that is used to remove the negative half component of the AC. This process is called the Rectification. Further, a 1000uF capacitor has been used for Filtration, meaning removing the ripples in the resulting wave. And the voltage regulator 7808 has been used to regulate the DC wave, to provide an uninterrupted and smooth 8V DC supply. The whole process of converting 220V AC into low-voltage DC, has been explained in this article: Cell Phone Charger Circuit

The second part of the emergency light circuit consists of the main functionality, that is to automatically switch ON the emergency light (Array of white LEDs) on Power Failure. We have used Relay here to automate this. A 6V, 4.5Ah rechargeable battery is connected to the Array of LEDs, through a Relay. Normally, when there is no power failure, the coil of the Relay remains energised, and the lever is attracted towards the NO (normally open) terminal, and the NC (normally connected) terminal remains open. In this situation, LEDs are disconnected from the rechargeable battery and remain OFF, also the battery is getting charged through the power supply from the transformer. A diode D5 is used to prevent the battery from flowing back. 

Now, when the power fails, the relay coil becomes de-energized and the lever gets connected to the NC terminal, which connects the LEDs to the rechargeable battery, and the LED array goes ON. This is how this emergency light works. Now, when the power is restored back, the relay gets activated and the lever again connects to the NO terminal, which in turn disconnects the LEDs from the battery and connects the battery to the transformer for charging. This is the circuit diagram of an emergency light 

Generally, 6v, 4.5Ah rechargeable battery comes with Deep discharge recovery and overcharge protection mechanisms, but we can use a zener diode of 6.8V to protect the battery from overcharging. We can also use other rechargeable batteries like Nickel-cadmium battery (NiCad), Nickel–metal hydride battery, cell phone batteries, etc. Further, we can also use the PNP transistor BD140 in place of the Relay. PNP transistor can be used here as a switch, like it will be OFF when a continuous voltage is applied to its base of it, in case when power is there and it will be ON, in case of power failure, which connects the LEDs to the rechargeable battery, and activates the LED emergency light.

This emergency light can also be made using an LDR (light-dependent resistor), in which light will automatically switch ON according to darkness, meaning it remains switched OFF in the presence of light and switches ON in the absence of light.

Uses and Advantages of this Automatic LED Emergency Light Project

An indispensable household electronic device for emergencies, this emergency light project offers dependable automatic operation during power outages. The project for an automated LED emergency light is ideal for:
 » Emergency lighting for homes during blackouts
 » Emergency lighting for offices and businesses
 » Automatic lighting in the garage and workshop
 » Electronics projects and education for students
 » Do-it-yourself emergency preparedness results 

Frequently Asked Questions

⇥ Can I increase the number of LEDs in this project for an automatic LED emergency light?
     You can increase the number of LEDs, but make sure the transformer rating doesn't exceed 500mA. Compute: For safe opera            tion, the total LEDs × 20mA should be ≤ 500mA.

⇥ How long does it take for the 6V battery in this emergency light circuit to charge?
    Using this circuit's charging mechanism, it normally takes 8–10 hours to fully charge a 6V 4.5Ah battery from a fully discharged       state.

⇥ In the event of a power outage, how long does the emergency light project battery last?
    A 6V 4.5Ah battery and four 20mA LEDs allow the emergency light to run continuously for more than 50 hours during a power         outage.

Related Emergency Light Projects

Check out our engineer-built emergency lighting projects in the gallery below —click to learn more.

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